Conventional nasal cannulae are used for the inhalation of oxygen or breathable gas mixtures containing oxygen. Some are aimed at semi-mobile users who can gain a degree of independence by using the cannulae together with mobile gas dispensers. Other users include those who work in hostile environments and require the delivery of a breathable gas whilst in the hostile environment.
Although the use of such nasal cannulae particularly for semi-mobile users are clearly advantageous, they can also present problems due to air entrainment with the subsequent dilution of the delivered gas.
This problem has been addressed by the use of masks which can regulate the amount of air entrained. The main drawbacks to the use of these known masks are:
uncomfortable to wear, leading possibly to necrosis
heavy and bulky
complicated to use
unaesthetic.
It is known from WO-A-92/20392 for a nasal cannula to include a tubular insert element having a distal portion to be placed in a nasal passage and a proximal portion for connection to a supply line for oxygen or an oxygen-enriched gas. The distal portion is formed of a flexible and resilient material and has a divergent, generally frusto-conical configuration. The cannula provides a positive and comfortable fit in the nasal passage and is conveniently used with high humidity, high flowrate oxygen-enriched air supplied by oxygen-concentrators employing gas separation membranes.
Although the tubular insert element is conical in shape, air can be entrained through the gap between the nasal passage and the cone thereby decreasing the oxygen concentration of the inhaled gas.
The present invention relates to nasal cannulae for the delivery of a gas or gas mixture under pressure to the nasal passages of a patient or user.
For the avoidance of doubt the use of the term xe2x80x9cgasxe2x80x9d throughout this specification is intended not only to embrace a single gas, for example, oxygen but also gas mixtures, for example, mixtures of oxygen/nitrogen or oxygen/helium.
It is an aim of the present invention to provide a nasal cannula which obviates or minimises these drawbacks and, furthermore in the case of the user working in a hostile environment, minimises the possibility of the entrainment of gases forming part of the hostile environment.
According to the present invention a nasal cannula for use in administering a gas under pressure through a nasal passage of a user comprises at least one tubular nasal prong assembly including
an inner tubular prong having a distal end to be placed in or adjacent the nasal passage and a proximal end for connection to a supply line for the gas and
an outer sleeve extending over at least a portion of the inner tubular prong to define with the inner tubular prong an annular passage, the annular passage being in communication with the supply line, the arrangement being such that when gas flows through the supply line most will pass through the distal end of the inner tubular prong for delivery to the nasal passage but some will pass through the annular passage to form a shielding stream.
In one embodiment, the outer sleeve is in the form of a shroud which extends over a portion of the inner tubular prong formed with an array of through holes (i.e. orifices), the arrangement being such that when gas from the supply line passes through the inner tubular prong most will be delivered to the distal end for delivery to the nasal passage but some will exit the array of holes in to the annular passage to form a shielding stream.
Preferably, the flow of gas through the array of holes is no more than 50% of the flow of gas leaving the distal end of the tubular nasal prong.
In a second embodiment the outer sleeve is in the form of a shroud which extends over a portion of the inner tubular prong and is spaced from the inner tubular prong by at least one support.